1. Field of the Invention
The present invention relates to a method of manufacturing blast furnace coke using briquette which is one of the coke manufacturing techniques.
2. Description of the Prior Art
With recent developments in the field of iron and steel industry, the demands for the principal raw materials such as coke are rapidly increasing. Thus, it has become more and more difficult to obtain hard coking coal of high quality essential to the manufacture of blast furnace coke due to the universal restriction of resources and high costs.
The fact has given the priority to the research and development of a method for manufacturing blast furnace coke of high quality using a blend of coal of relatively low grade such as non coking or poorly coking coal. These coals have so far been considered unfit for the manufacture of blast furnace coke. In addition, blends of larger amounts of soft coking coal and various caking substance or manufacturing methods using such substances have been proposed.
A method of manufacturing coke by obtaining briquettes, blending it in the portion of coal ready for coke oven charging and carbonizing the blend has been proposed for a possible solution of the above problem. The prior art methods of manufacturing briquettes use a caking substance of bituminous material with a softening point at around 60.degree. to 80.degree. C. The blend is mixed with a mixer such as a pug mill, i.e., a low speed rotating type mixer having a mixing tool with the peripheral speed at 5.0 m/sec or lower, while steam at 120.degree. to 250.degree. C. is being blown into the blend, and is then briquetted. Important factors involved in these methods are the adjustment of the softening point of the caking substance, the temperature of the blown steam and mixing duration. A mixing duration of around 4 to 10 minutes is employed for the industrial scale due to various restrictions. Accordingly, to maintain the strength of the briquette, a caking substance having a suitable softening point corresponding to the temperature of the steam must be selected and a great amount of steam must be applied. In practice, however, when a low speed rotating type mixer such as a pug mill is used, even if the softening point of the caking substance and the steam consumption are well adjusted, the mixture immediately before briquetting will not be mixed to a satisfactory uniformity. This is evident from the fact that the inventors of the present invention noted in their experiments wherein tar sludge produced in the coke manufacturing process is used as raw material for briquetting, scattering in the quality of briquette when the mixing duration was shorter than a certain period, i.e., 5 minutes or preferably longer than 7 minutes, with a double shaft, one stage pug mill, while the quality of briquette mixed for the above duration was found to be stable.
Therefore, to obtain a throughly uniform mixture by the use of a low speed rotating type mixer with low mixing efficiency such as pug mill, it is preferable to utilize as long mixing duration as possible. The method, therefore, requires a mixer and, accordingly, a steam generator large in size. Consequently, the costs for the plant construction are increased and the plant may be subjected to various severe restrictions for pollution control.